Mammalian glutaredoxins (GRX) are members of the thiol-disulfide oxidoreductase family. They are often characterized by a thioredoxin fold and a Cys-Pro (Ser)-Tyr-Cys active site (SEQ ID NO:1). Examples include GRX1, a cytosolic protein, and GRX2, which may be directed to the mitochondria by a mitochondrial leader sequence and/or can also occur in the nucleus following alternative splicing. Mammalian glutaredoxins may specifically catalyze the reversible reduction of protein-glutathionyl-mixed disulfides to free sulfhydryl groups, using glutathione (GSH) as a cofactor.